New to building websites. Do you need to have some type of .htaccess file to secure it on a simple html site?
Not sure what you are asking here, but you don’t need anything in an htaccess file, per se. They are handy for various things, though.
I just uploaded a site and was wondering if I had to secure it’s files somehow.
No, not really. What do you mean by “secure”? Is there something in particular you want to do?
No I just don’t want anyone to be able to change anything.
No, normally no one can change your site unless you give them some kind of access. 
They can’t unless they can get access (legally or not) to your server
I’d advise changing your file and directory permissions to read-only, for added security.
(I had a couple of sites hacked a few years back, and files were uploaded which I knew nothing about. With directory permissions set to read-only, even I can’t upload to those folders, unless I remember to change them first. Which, of course, I always do. 
)